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The experimental investigation of heat transfer analysis in pin-fin array has been attempted. The pin-fin array and base plate are arranged in in-line which is made of Dura-aluminum. Pins having constant height, diameter and pitch...
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The experimental investigation of heat transfer analysis in pin-fin array has been attempted. The pin-fin array and base plate are arranged in in-line which is made of Dura-aluminum. Pins having constant height, diameter and pitch were employed in stream wise direction (S_y/L=0.2). Pitch in span wise direction and pin tip to shroud clearance were varied and the results are reported with and without bypass. A constant temperature was maintained in base plate and pins for all experimental conditions. A better performance has been achieved with S_x/W=0.048 than other higher pitches having pin tip to shroud clearance is zero (without bypass). Higher heat removal rate is achieved at higher velocities.
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The current paper aimed to investigate the primary control mechanism of various Nanosecond Dielectric Barrier Discharge (NS-DBD) plasma actuators on the Shock Wave/Boundary Layer Interaction (SWBLI). For this purpose, the effects ...
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The current paper aimed to investigate the primary control mechanism of various Nanosecond Dielectric Barrier Discharge (NS-DBD) plasma actuators on the Shock Wave/Boundary Layer Interaction (SWBLI). For this purpose, the effects of the NS-DBD actuator have been investigated on an M=2.8 supersonic flow numerically. The Reynolds Averaged Navier-Stokes (RANS) equations and SST turbulence model were used as the governing equations to simulate the supersonic flow characteristics. The numerical simulation of the baseline flow (without plasma actuator) was verified using an investigation on wall pressure distribution and the size of SWBLI. Then, NS-DBD phenomenological model based on the energy deposition model in accordance with experimental data was applied to the baseline simulation. Moreover, various stream-wise and span-wise NS-DBD plasma actuator models were used to investigate the actuator effects on the studied flow’s low-density separation zone. Comparing the numerical results of the stream-wise and span-wise actuations revealed that both actuator types cause a momentum transferred to the flow, consequently decreasing the SWBLI region’s size and the boundary layer’s thickness. The results showed that the presence of the NS-DBD actuator increased the local temperature of flow over the insulated electrode. In this regard, a stream-wise NS-DBD actuator with a length of 90 mm upstream of the SWBLI increased the separation flow velocity by 33.7% and decreased the length of the separation region by 5 mm. Also, in this case, after 170 microseconds from the start of actuation, the size of SWBLI decreased by 4.2 mm. Therefore, it can be concluded that the stream-wise type of actuation was more effective in reducing the flow separation and SWBLI size than the span-wise type due to vortex generation into the inlet flow and suppressing the SWBLI region. The proposed NS-DBD actuators were mainly capable of applying the momentum to the boundary layer and reducing the velocity of separated flow in the SWBLI zone. The micro shock wave propagation through the flow associated with the NS-DBD discharge of the actuators can produce more effective high-speed flow control.
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In this paper we introduce a general framework that exponentially improves the space, degree of independence, and time needed by min-wise-based algorithms. The authors, in SODA '11 [1], introduced an exponential time improvement f...
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In this paper we introduce a general framework that exponentially improves the space, degree of independence, and time needed by min-wise-based algorithms. The authors, in SODA '11 [1], introduced an exponential time improvement for min-wise-based algorithms. Here we develop an alternative approach that achieves both exponential time and exponential space improvement. The new approach relaxes the need for approximately min-wise hash functions, hence getting around the Ω(log 1/∈) independence lower bound, by defining and constructing a d-k-min-wise independent family of hash functions; surprisingly, for most cases, only 8-wise independence is needed for the additional improvement. Furthermore, we discuss how this construction can be used to improve many min-wise-based algorithms. To our knowledge such definitions, for hash functions, were never previously studied or constructed. Finally, we show how to apply it for similarity and rarity estimation over data streams; other min-wise-based algorithms can be adjusted in the same way.
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SNOW-V is a new member in the SNOW family of stream ciphers, hoping to be competitive in the 5G mobile communication system. In this paper, we study the resistance of SNOW-V against bitwise fast correlation attacks by constructing...
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SNOW-V is a new member in the SNOW family of stream ciphers, hoping to be competitive in the 5G mobile communication system. In this paper, we study the resistance of SNOW-V against bitwise fast correlation attacks by constructing bitwise linear approximations. First, we propose and summarize some efficient algorithms using the slice-like techniques to compute the bitwise linear approximations of certain types of composition functions composed of basic operations like ?, ⊕, Permutation, and S-box, which have been widely used in word-oriented stream ciphers such as SNOW-like ciphers. Then, using these algorithms, we find a number of stronger linear approximations for the FSM of the two variants of SNOW-V given in the design document, i.e., SNOW-V σ0 and SNOW-V?8, ?8. For SNOW-V σ0, where there is no byte-wise permutation, we find some bitwise linear approximations of the FSM with the SEI (Squared Euclidean Imbalance) around 2?37.34 and mount a bitwise fast correlation attack with the time complexity 2251.93 and memory complexity 2244, given 2103.83 keystream outputs, which improves greatly the results in the design document. For SNOW-V?8, ?8, where both of the two 32-bit adders in the FSM are replaced by 8-bit adders, we find our best bitwise linear approximations of the FSM with the SEI 2?174.14, while the best byte-wise linear approximation in the design document of SNOW-V has the SEI 2?214.80. Finally, we study the security of a closer variant of SNOW-V, denoted by SNOW-V?32, ?8, where only the 32-bit adder used for updating the first register is replaced by the 8-bit adder, while everything else remains identical. For SNOW-V?32, ?8, we derive many mask tuples yielding the bitwise linear approximations of the FSM with the SEI larger than 2?184. Using these linear approximations, we mount a fast correlation attack with the time complexity 2377.01 and a memory complexity 2363, given 2253.73 keystream outputs. Note that neither of our attack threatens the security of SNOW-V. We hope our research could further help in understanding bitwise linear approximation attacks and also the structure of SNOW-like stream ciphers.
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In this paper we introduce a general framework of related-key attack on block-wise stream ciphers which are suitable for the protection of multimedia and ubiquitous systems. As a case study, we show how our cryptanalytic framework...
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In this paper we introduce a general framework of related-key attack on block-wise stream ciphers which are suitable for the protection of multimedia and ubiquitous systems. As a case study, we show how our cryptanalytic framework is applied to a block-wise stream cipher TWOPRIME: we construct various related-key differentials of TWOPRIME and use them to show that recovering related keys of TWOPRIME can be performed with a data complexity of 2~(14) known plaintext blocks and a time complexity of 2~(32) 8-bit table lookups. We expect that our general framework for a related-key attack would be useful tool for analyzing many of block-wise stream ciphers.
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Video-based action recognition has become a challenging task in computer vision and attracted extensive attention from the academic community. Most existing methods for action recognition treat all spatial or temporal input featur...
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Video-based action recognition has become a challenging task in computer vision and attracted extensive attention from the academic community. Most existing methods for action recognition treat all spatial or temporal input features equally, thus ignoring the difference of contribution provided by different features. To address this problem, we propose a spatial-temporal channel-wise attention network (STCAN) that is able to effectively learn discriminative features of human actions by adaptively recalibrating channel-wise feature responses. Specifically, the STCAN is constructed on a two-stream structure and we design a channel-wise attention unit (CAU) module. Two-stream network can effectively extract spatial and temporal information. Using the CAU module, the interdependencies between channels can be modelled to further generate a weight distribution for selectively enhancing informative features. The network performance of STCAN has been evaluated on two typical action recognition datasets, namely UCF101 and HMDB51, and comparable experiments have been performed to demonstrate the effectiveness of the proposed STCAN.
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In this paper, we study and compare the byte-wise and bitwise linear approximations of SNOW 2.0 and SNOW 3G, and present a fast correlation attack on SNOW 3G by using our newly found bitwise linear approximations. On one side, we ...
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In this paper, we study and compare the byte-wise and bitwise linear approximations of SNOW 2.0 and SNOW 3G, and present a fast correlation attack on SNOW 3G by using our newly found bitwise linear approximations. On one side, we reconsider the relation between the large-unit linear approximation and the smallerunit/ bitwise ones derived from the large-unit one, showing that approximations on large-unit alphabets have advantages over all the smaller-unit/bitwise ones in linear attacks. But then on the other side, by comparing the byte-wise and bitwise linear approximations of SNOW 2.0 and SNOW 3G respectively, we have found many concrete examples of 8-bit linear approximations whose certain 1-dimensional/bitwise linear approximations have almost the same SEI (Squared Euclidean Imbalance) as that of the original 8-bit ones. That is, each of these byte-wise linear approximations is dominated by a single bitwise approximation, and thus the whole SEI is not essentially larger than the SEI of the dominating single bitwise approximation. Since correlation attacks can be more efficiently implemented using bitwise approximations rather than large-unit approximations, improvements over the large-unit linear approximation attacks are possible for SNOW 2.0 and SNOW 3G. For SNOW 3G, we make a careful search of the bitwise masks for the linear approximations of the FSM and obtain many mask tuples which yield high correlations. By using these bitwise linear approximations, we mount a fast correlation attack to recover the initial state of the LFSR with the time/memory/data/pre-computation complexities all upper bounded by 2174.16, improving slightly the previous best one which used an 8-bit (vectorized) linear approximation in a correlation attack with all the complexities upper bounded by 2176.56. Though not a significant improvement, our research results illustrate that we have an opportunity to achieve improvement over the large-unit attacks by using bitwise linear approximations in a linear approximation attack, and provide a newinsight on the relation between large-unit and bitwise linear approximations.
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In this paper, we studied the convective heat transfer from a stream-wise oscillating circular cylinder. Two dimensional numerical simulations are conducted at Re = 100-200, A = 0.1-0.4 and F=f_o/f_s = 0.2-3.0 with the aid of the ...
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In this paper, we studied the convective heat transfer from a stream-wise oscillating circular cylinder. Two dimensional numerical simulations are conducted at Re = 100-200, A = 0.1-0.4 and F=f_o/f_s = 0.2-3.0 with the aid of the lattice Boltzmann method. In particular, detailed attentions are paid on the extensive numerical results elucidating the influence of oscillation frequency, oscillation amplitude and Reynolds number on the time-average and RMS value of the Nusselt number. Over the ranges of conditions considered herein, the heat transfer characteristics are observed to be influenced in an intricate manner by the value of the oscillation frequency (F), oscillation amplitude (A) and Reynolds number (Re). Firstly, the heat transfer is enhanced when the cylinder oscillates stream-wise with small amplitude and low frequency, while it will be reduced by large amplitude and high frequency. Secondly, the average Nusselt number (Nu (ave)) decreases against the increasing value of oscillation frequency, while the RMS value of the Nusselt number, Nu (RMS), displays an opposite trend. Third, we obtained a similar frequency effect on the heat transfer over the range of Reynolds numbers investigated in this paper. In addition, detailed analyses on phase portraits, energy spectrum are also made.
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The evolution of low-aspect-ratio rectangular synthetic jets is investigated with dye and laser-induced-fluorescence (LIF) flow visualization techniques. This paper analyzes the impacts of three key parameters on the evolution of ...
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The evolution of low-aspect-ratio rectangular synthetic jets is investigated with dye and laser-induced-fluorescence (LIF) flow visualization techniques. This paper analyzes the impacts of three key parameters on the evolution of vortical structures, respectively, including orifice aspect-ratio (AR), dimensionless stroke length, and Reynolds number. Compared with circular synthetic jet, all the rectangular synthetic jets display vortex ring axis switching, and may develop into two types of stream-wise vortices I and II. The evolution of the vortex ring and the generation of stream-wise vortices are influenced by three parameters. In particular, stream-wise vortices are not detected for a low AR, stroke length or Reynolds number case.
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This paper reports the results of combined experimental and numerical study of laminar conjugate natural convection heat transfer from four planar heat generating elements arranged in tandem and placed symmetrically in a vertical ...
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This paper reports the results of combined experimental and numerical study of laminar conjugate natural convection heat transfer from four planar heat generating elements arranged in tandem and placed symmetrically in a vertical channel. The heat transfer characteristics of the downstream heat generating elements affected by the natural convection plume arising from the upstream heat generating elements are explored. The dependence of modified Rayleigh number, channel aspect ratio and stream-wise height ratio on heat transfer characteristics of the heat generating elements is analysed and discussed. The mathematical model governing the problem is numerically solved in a three-dimensional computational domain using a commercial computational fluid dynamic package FLUENT 6.3. Numerical simulations have been carried out for modified Rayleigh number in the range 2.0 × 10~6-8.1 × 10~7. The comparison of experimental and numerical results is reasonably in good agreement. Correlations for average convective Nusselt number of individual heat sources as a function of modified Rayleigh number, channel aspect ratio and stream-wise height ratio are reported.
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